This invention relates to an electrical contact apparatus.
In a prior art contact apparatus known from German Pat. specification No. 1,055,712, a resiliently mounted movable contact cooperates with a counter contact that is also resiliently mounted. In the rest position of the apparatus, a massive body which is again resiliently mounted rests against the counter contact at the side remote from the movable contact. When the movable contact is actuated by exciting a solenoid and hits the counter contact, the kinetic energy of the movable contact is transmitted through the counter contact onto the massive body. Under the condition that the masses of the movable contact and the massive body are substantially equal, the movable contact and the counter contact will retain no kinetic energy and the counter contact will remain in its rest position so that the contact is held closed without bouncing as long as the excitation of the solenoid persists. The massive body is deflected in the impact direction by the kinetic energy transmitted to it, thereby moving away from the rear side of the counter contact.
To prevent the massive body from subsequently swinging back and again transmitting its energy to the contact couple, one embodiment of the prior art apparatus includes a permanent magnet which holds the massive body in its deflected position. In this case, the massive body is returned from its rest position by means of a bracket which pulls the massive body away from the permanent magnet, the bracket being fixed to the movable contact so as to return with the same when the excitation of the solenoid is switched off. This mechanism, however, requires the spring carrying the movable contact to excert a high resetting force, so that this contact apparatus is suited only for such applications in which a high actuating force is available.
In another embodiment of the prior art contact apparatus, the massive body is connected to the piston of a damping cylinder, the piston being provided with valves that are open when the piston moves in the deflecting direction and are closed during return movement, thereby damping the return movement. The damping mechanism provided in this case, however, it too expensive and bulky for many applications.
A disadvantage common to both of the prior art locking or damping mechanisms further resides in the fact that they considerably reduce the maximum switching frequency because the massive body is delayed in returning to its starting position.
German patent specification No. 972,236 discloses a further electrical contact apparatus which exploits the physical principle of the elastic impact, but it does so for achieving a fast-switching behaviour rather than for avoiding contact bouncing.